Radio receiver



July 14, 1942. H. GIBAS 2,289,771

RADIO RECEIVER Filed Oct. 26, 1940' 2 DETECTOR AFI AMPL/F/ER INVENTQ R I HUBERT 8/16 ATTORNEY Patented July 14, 1942 RADIO RECEIVER Hubert Gibas, Berlin, Germany, assignor to Telefunken Gesellschaft fiir Drahtlose Telegraphic, m. b. IL, Berlin, Germany, a corporation of Germany Application October 26, 1940, Serial No.,362,889 In Germany August '7, 1939 6 Claims. (Cl. 250-20) It is known to provide in receivers a severable positive feedback in the radio frequency part and intermediate frequency part. There is then obtainable at will high amplification and high selectivity, or lower amplification and more favorable reproduction.

Furthermore, it is known in order to reduce distortion and to obtain a definite frequency characteristic in the audio frequency part, to provide negative feedback (countercoupling). Since the negative feedback decreases the amplification at the same time, it can be adapted for selective disconnection for attaining the highest amplification. When coupling the switches for the positive and negative feedback, it is possible to obtain at will the highest possible amplification at a favorable selectivity and fair reproduction, or the best reproduction at low amplification and low selectivity.

The present invention deals with the underlying problem of simplifying such a circuit arrangement; in other words, to render possible the switching with the least possible effort.

The present invention relates to a receiver with severable positive feedback in the high frequency section, or intermediate frequency section, whereby said feedback acts from the anode, or from the screen grid, of a receiver detector tube across a condenser and across a feedback coil upon the coil of the grid circuit.

In accordance with the present invention, in order to switch-in at the same time a negative audio frequency feedback from a following audio frequency amplifier tube, the lead-in for the negative feedback is connected by the same switch placed in series to the feedback coil, to the end of the positive feedback condenser which faces away from the anode, or from the screen grid, of the receiving detector, instead of connecting said lead-in to the anode, or screen grid, of said detector.

The accompanying figure shows an example of construction of the present invention.

The intermediate frequency (I. F.) signal is applied across an I. F. band pass filter B to the grid of the detector tube I. The audio frequency voltage obtained through detection is then applied across a resistance coupling to the end tube 2. The positive feedback acts from the anode of the tube 1 through the condenser C, switch S and feedback ccilRKupon the secondary circuit of the band filter B. The negative feedback takes place across the ohmic resistance R which is placed at the left end of the condenser C instead of being connected to the anode of the tube l.

When the switch S is open the negative feedback acts through the condenser 0 back upon the input of the tube 2. At closed position of switch S, on the one hand, the positive feedback is effective, and,'0n the other hand, the negative feedback is shortcircuited by the feedback coil RK as regards audio frequency and thus is ineffective. At open position of the switch, therefore, the negative feedback is active.

In order to reduce the negative feedback for the low audio frequencies a condenser C1 may, in a known manner, be placed in series to the resistance R. When utilizing the present invention this condenser C1 may be dispensed with through so dimensioning the condenser C that the desired frequency characteristic is attained. The resistance R has a value of, for instance, 2 megohms and the condenser C a value of 500 microfarads. In this case the desired magnitude of the feedback is attained by a corresponding dimensioning of the feedback coil.

What is claimed is:

1. In a high frequency circuit comprising a tube having at least a cathode, control grid and ouput electrode, a high frequency input network connected between the grid and cathode, a feedback path connected between the output electrode and said input network, said path including a reactance in series with a switch device, an output network connected to said output electrode, a second feedback path between said output network and a point between said reactance and switch whereby when said switch is opened to render said first path ineffective the second path is concurrently rendered effective.

2. In a high frequency circuit comprising a tube having at least a cathode, control grid and output electrode, a high frequency input network connected between the grid and cathode, a regenerative feedback path connected between the output electrode and said input network, said path including a reactance in series with a switch device, an output network connected to said output electrode, a second degenerative feedback path between said output network and a point between said reactance and switch whereby when said switch is opened to render said first path ineffective the second path is concurrently rendered effective.

3. In a high frequency circuit comprising a tube having at least a cathode, control grid and output electrode, a high frequency input network connected between the grid and cathode, a feedback path connected between the output electrode and said input network, said path including a capacitative reactance in series with a switch device, an output network connected to said output electrode, a second feedback path including a resistive impedance between said output network and a point between said reactance and switch whereby when said switch is opened to render said first path ineffective the second path is concurrently rendered effective.

4. In a system comprising a detector having a tube provided with input electrodes and output electrodes, a signal input circuit connected between the input electrodes, an audio network connected to said output electrodes, a regenerative signal feedback path connected from the output electrode to said input circuit, said patl'i including a reactance in series with a switch device connected to the low potential side of the input circuit, a degenerative audio-voltage feedback path between said audio network and said switch device whereby actuation of the latter renders one or the other of said feedback paths effective in mutually exclusive fashion.

5. In a system comprising a detector having a tube provided with input electrodes and output electrodes, a signal input circuit connected between the input electrodes, an audio network connected to said output electrodes, a regenerative signal feedback path connected from the output electrode to said input circuit, said path including a reactance in series with a switch device connected to the low potential side of the input circuit, a degenerative audio voltage feedback path between said audio network and a point intermediate the said reactance and said switch device whereby actuation of the latter renders one or the other of said feedback paths effective in mutually exclusive fashion.

6. In a system comprising a detector having a tube provided with input electrodes and output electrodes, a signal input circuit connected between the input electrodes, an audio network connected to said output electrodes, a regenera tive signal feedback path connected from the output electrode to said input circuit, said path including a capacitative reactance in series with a switch device connected to the low potential side of the input circuit, a degenerative audio voltage feedback path comprising a resistor in series with a condenser connected between said audio network and said switch device whereby actuation of the latter renders one or the other of said feedback paths effective in mutually exclusive fashion.

HUBERT GIBAS. 

